A year ago, China's light-emitting diode industry seemed like a case study of industrial policy gone awry. Hundreds of factories built all over eastern China, often with lavish clean energy subsidies from state-owned banks and local governments, were operating at half capacity. The share prices of LED manufacturers were plunging. Now demand is surging, and the Chinese manufacturers suddenly find their factories running at full tilt, churning out LEDs faster and cheaper than global rivals.

With a price war underway, the Chinese are taking share from top players in the United States, Europe and Japan, the industry pioneers that made crucial technological breakthroughs, and from Taiwan and South Korea, previously the leaders in low-priced LEDs.

For some in the United States, the Chinese expansion has uncomfortable echoes of the solar panel and wind turbine industries, in which China went from a bit player to global leader through a combination of extensive government subsidies and low-interest loans from state-owned banks.